Technical field
[0001] The present invention relates to an epoxy resin composition for fiber-reinforced
composite materials production serving to provide a fiber-reinforced composite material
having high compressive strength after impact, interlaminar toughness, and compressive
strength under heat and humidity conditions, and a prepreg and a fiber-reinforced
composite material produced therefrom.
Background art
[0002] High in specific strength and specific rigidity, carbon fiber-reinforced composite
materials are useful and have been used in a wide variety of applications including
aircraft structure members, windmill blades, automobiles' exterior plates, and computer
parts such as IC trays and notebook computer housing, and demands for them have been
increasing every year.
[0003] A carbon fiber-reinforced composite material has an heterogeneous materials produced
by molding a prepreg consisting essentially of carbon fibers, i.e., reinforcement
fibers, and a matrix resin, and accordingly, there are large differences between the
physical properties in the direction of the aligned reinforcement fibers and those
in other directions. For instance, it is known that the interlaminar toughness, which
represents the resistance to interlaminar fracture of the reinforcement fiber layers,
cannot be improved drastically by simply increasing the strength of the reinforcement
fibers. In particular, carbon fiber-reinforced composite materials containing a thermosetting
resin as matrix resin are generally liable to be fractured easily by a stress caused
in a direction other than the alignment direction of the reinforcement fibers, reflecting
the low toughness of the matrix resin. In this respect, various techniques have been
proposed aiming to provide composite materials that have improved physical properties,
including interlaminar toughness, to resist a stress in directions other than the
alignment direction of the reinforcement fibers while maintaining high compressive
strength in the fiber direction under high temperature and high humidity conditions,
which is required for aircraft structural members.
[0004] Furthermore, fiber-reinforced composite materials have recently been applied to an
increased range of aircraft structural members, and fiber-reinforced composite materials
are also in wider use for windmill blades and various turbines designed to improve
power generation efficiency and energy conversion efficiency. Studies have been made
to provide thick members produced from prepregs consisting of an increased number
of layers as well as members having three-dimensionally curved surfaces. If such a
thick member or curved-surfaced member suffers from a load, i.e., tensile or compressive
stress, the prepreg fiber layers may receive a peeling stress generated in an antiplane
direction, which can cause opening-mode interlayer cracks. As these cracks expand,
the overall strength and rigidity of the member can deteriorate, possibly leading
to destruction of the entire member. Opening-mode, that is, mode I, interlaminar toughness
is necessary to resist this stress.
[0005] Compared to this, there is a proposal of a technique that uses high-toughness particle
material of, for example, polyamide provided in regions between fiber layers so that
the mode II interlaminar toughness will be increased to decrease the degree of damage
that can be caused in falling weight impact test for the surface (see patent document
1). Even this technique, however, cannot serve adequately in the case of mode I interlaminar
toughness.
[0006] Apart from this, a material with high interlaminar shear strength under heat and
humidity conditions as well as high impact resistance has been disclosed in which
sphericity particles of polyamide resin, namely, Grilamid, is provided in regions
between fiber layers while an elastomer, block copolymer, or the lilke, such as butadiene-acrylonitrile
copolymer, is used to increase the toughness of the matrix resin (see patent document
2). Even this technique, however, cannot serve adequately to achieve both high mode
I interlaminar toughness and high mode II interlaminar toughness at the same time.
There is another proposal that discloses a material with both high impact resistance
and high tensile strength in which polyamide particles containing nylon 6 and nylon
12 are provided in regions between fiber layers while thermoplastic resin such as
polyethersulfone is used to increase the toughness of the matrix resin (see patent
document 3). Even this technique, however, cannot serve adequately to achieve high
mode I interlaminar toughness and high compressive strength in the fiber direction
under heat and humidity conditions.
Prior art documents
Patent documents
Summary of the invention
Problems to be solved by the invention
[0008] An object of the present invention is to provide an epoxy resin composition serving
to produce a fiber-reinforced composite material having high mode I interlaminar toughness
and high mode II interlaminar toughness as well as compressive strength under heat
and humidity conditions, and a prepreg and a fiber-reinforced composite material produced
therefrom.
Means of solving the problems
[0009] The present invention adopts any of the following constitutions to meet the above
object. Epoxy resin composition for fiber-reinforced composite material production,
including at least the following components [A], [B], [C], and [D]:
- [A] epoxy,
- [B] resin particles insoluble in epoxy resin and meeting the following requirements,
(b 1) to (b3):
(b1) the particles have a diameter distribution index of 1.0 to 1.8,
(b2) the particles have a sphericity of 90 or more, and
(b3) the particles have a glass transition temperature of 80 to 180°C,
- [C] at least one elastomer component selected from the group consisting of rubber
particles and block copolymers containing a block with a glass transition temperature
of 20°C or less,
- [D] epoxy resin curing agent.
[0010] In a preferred embodiment of the epoxy resin composition for fiber-reinforced composite
material production according to the present invention, the above-mentioned epoxy
resin [A] contains a polyfunctional amine type epoxy resin and/or a bifunctional amine
type epoxy.
[0011] In another preferred embodiment of the epoxy resin composition for fiber-reinforced
composite material production according to the present invention, resin particles
[B] have an average particle diameter of 8 to 35 µm, or resin particles [B] are particles
of polyamide having a chemical structure as represented by general formula (1).
[0012]

[0013] (In the formula, R
1 and R
2 represent a hydrogen atom, an alkyl group containing 1 to 8 carbon atoms, or a halogen
atom, and may be either identical to or different from each other. In the formula,
R
3 represents a methylene group containing 1 to 20 carbon atoms, or a phenylene group).
[0014] In another preferred embodiment of the epoxy resin composition for fiber-reinforced
composite material production according to the present invention, epoxy resin curing
agent [D] is an aromatic amine, specifically, diaminodiphenyl sulfone, a derivative
thereof, or an isomer thereof.
[0015] In another preferred embodiment of the epoxy resin composition for fiber-reinforced
composite material production according to the present invention, elastomer component
[C] is at least one block copolymer selected from the group consisting of those having
a structure of S-B-M, B-M, or M-B-M.
(Here, each of the aforementioned blocks is connected to an adjacent one via a covalent
bond, or via an intermediary molecule that is connected to the block via a covalent
bond and connected to the adjacent one via another covalent bond. Block M includes
a homopolymer of polymethyl methacrylate or a copolymer in which at least 50 wt% is
accounted for by methyl methacrylate, and block B is incompatible with block M and
has a glass transition temperature of 20°C or less. Block S is incompatible with blocks
B and M and has a glass transition temperature that is higher than the glass transition
temperature of block B.))
According to the present invention, furthermore, the aforementioned epoxy resin composition
for fiber-reinforced composite material production can be impregnated into reinforcement
fibers to produce prepreg, and the epoxy resin composition for fiber-reinforced composite
material production or the prepreg can be cured to produce a fiber-reinforced composite
material.
Effect of the invention
[0016] According to the present invention, it is possible to provide a fiber-reinforced
composite material having high mode I interlaminar toughness, high mode II interlaminar
toughness, and compressive strength under heat and humidity conditions, as well as
an epoxy resin composition for fiber-reinforced composite material production and
a prepreg that serve for production thereof.
Description of embodiments
[0017] Described in detail below are the epoxy resin composition for fiber-reinforced composite
material production, prepreg, and fiber-reinforced composite material according to
the present invention.
[0018] Epoxy resin [A] designed for the present invention is a compound having a plurality
of epoxy groups in one molecule.
[0019] Specific examples of epoxy resin [A] to be used for the present invention include
aromatic glycidyl ethers produced from a phenol with a plurality of hydroxyl groups,
aliphatic glycidyl ethers produced from alcohol with a plurality of hydroxyl groups,
glycidyl amines produced from amine, glycidyl esters produced from a carboxylic acid
with a plurality of carboxyl groups, and epoxy resin with an oxirane ring.
[0020] In particular, glycidyl amine type epoxy resins are preferred because they are low
in viscosity and able to impregnate reinforcement fibers easily and accordingly can
serve to produce fiber-reinforced composite materials with good mechanical characteristics
including heat resistance and elastic modulus. Such glycidyl amine type epoxy resins
can be roughly divided into two groups: polyfunctional amine type epoxy resins and
bifunctional amine type epoxy resins.
[0021] A polyfunctional amine type epoxy resin is an amine type epoxy containing three or
more epoxy groups in one epoxy resin molecule. Such polyfunctional amine type epoxy
resins include, for instance, tetraglycidyl diaminodiphenyl methane, triglycidyl aminophenol,
tetraglycidyl xylylene diamine, and diglycidyl aniline, as well as halogen-substituted
compounds, alkyl-substituted compounds, aralkyl-substituted compounds, allyl-substituted
compounds, alkoxy-substituted compounds, aralkoxy-substituted compounds, allyloxy-substituted
compounds, and hydrogenated compounds thereof.
[0022] There are no specific limitations on the polyfunctional amine type epoxy resin to
be used, but preferred ones include tetraglycidyl diaminodiphenyl methane, triglycidyl
aminophenol, tetraglycidyl xylylene diamine, and substituted or hydrogenated ones
thereof.
[0023] Useful tetraglycidyl diaminodiphenyl methanes as described above include "Sumiepoxy
(registered trademark)" ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), YH434L
(manufactured by Nippon Steel Chemical Co., Ltd.), "jER (registered trademark)" 604
(manufactured by Mitsubishi Chemical Corporation), and "Araldite (registered trademark)"
MY720 or MY721 (both manufactured by Huntsman Advanced Materials Gmbh). Useful triglycidyl
aminophenols and alkyl-substituted compounds thereof include "Sumiepoxy (registered
trademark)" ELM100 or ELM120 (manufactured by Sumitomo Chemical Co., Ltd.), "Araldite
(registered trademark)" MY0500, MY0510, or MY0600 (manufactured by Huntsman Advanced
Materials Gmbh), and "jER (registered trademark)" 630 (manufactured by Mitsubishi
Chemical Corporation). Useful tetraglycidyl xylylene diamines and hydrogenated-compounds
include "Tetrad (registered trademark)" -X and "Tetrad (registered trademark)" -C
(manufactured by Mitsubishi Gas Chemical Co., Inc.)
[0024] There are no specific limitations on the bifunctional amine type epoxy resin to be
used, but preferred ones include diglycidyl anilines and substituted- or hydrogenated-compounds
thereof. Examples of such diglycidyl anilines include GAN (manufactured by Nippon
Kayaku Co., Ltd.), and examples of alkyl-substituted diglycidyl aniline include GOT
(manufactured by Nippon Kayaku Co., Ltd.). Furthermore, allyloxy-substituted diglycidyl
anilines include, for instance, N,N-diglycidyl-4-phenoxy aniline, N,N-diglycidyl-4-(4-methyl
phenoxy) aniline, N,N-diglycidyl-4-(4-tert-butyl phenoxy) aniline, and N,N-diglycidyl-4-(4-phenoxy
phenoxy) aniline.
[0025] Polyfunctional amine type epoxy resin is used preferably as epoxy resin [A] for the
present invention because it can produce a cured resin with well-balanced mechanical
characteristics including heat resistance and elastic modulus. It is preferable that
such a polyfunctional amine type epoxy resin account for 40 to 70 mass% of the total
epoxy resin weight.
[0026] Bifunctional amine type epoxy resin is used preferably as epoxy resin [A] for the
present invention because it can serve to provide a resin composition with low viscosity
and a cured resin with high elastic modulus. It is preferable that such a bifunctional
amine type epoxy resin account for 15 to 40 mass% of the total epoxy resin weight.
It is also preferable to use such a bifunctional amine type epoxy resin in combination
with a polyfunctional amine type epoxy resin because it serves to achieve an improved
balance among viscosity, heat resistance, and other mechanical characteristics.
[0027] Epoxy resin [A] to be used for the present invention may contain other components
such as an epoxy resin that is not of a glycidyl amine type and a copolymer of an
epoxy resin and a thermosetting resin. Examples of the aforementioned thermosetting
resin to be copolymerized with an epoxy resin include, for instance, unsaturated polyester
resin, vinyl ester resin, epoxy resin, benzoxazine resin, phenol resin, urea resin,
melamine resin, and polyimide resin. These resin compositions and compounds may be
used singly or in combination.
[0028] Preferred epoxy resins that can be used as a non-glycidyl amine type epoxy resin
as described above include bifunctional epoxy resins such as glycidyl ether type epoxy
resin produced from a phenol as precursor. Such epoxy resins include bisphenol A type
epoxy resin, bisphenol F-type epoxy resin, bisphenol S type epoxy resin, naphthalene
type epoxy resin, biphenyl type epoxy resin, urethane modified epoxy resin, hydantoin-type
epoxy resin, and resorcinol type epoxy resin.
[0029] Being low in viscosity, a liquid bisphenol A type epoxy resin, bisphenol F-type epoxy
resin, or resorcinol type epoxy resin should preferably be used in combination with
another epoxy resin.
[0030] Compared to liquid bisphenol A type epoxy resins, solid-state bisphenol A type epoxy
resins will produce a structure with a low crosslink density, which will be low in
heat resistance but high in toughness, and accordingly they are used in combination
with a glycidyl amine type epoxy resin, liquid-state bisphenol A type epoxy resin,
or bisphenol F-type epoxy resin.
[0031] An epoxy resin with a naphthalene backbone will give a cured resin with a low water
absorption percentage and a high heat resistance. In addition, biphenyl type epoxy
resins, dicyclopentadiene-type epoxy resins, phenol aralkyl-type epoxy resins, and
diphenyl fluorene type epoxy resins are also preferred because they give cured resin
with a low water absorption percentage. Urethane modified epoxy resins and isocyanate
modified epoxy resins give cured resins with a high fracture toughness and a high
extensibility.
[0032] Commercial products of bisphenol A type epoxy resin include "EPON (registered trademark)"
825 (manufactured by Mitsubishi Chemical Corporation), "EPICLON (registered trademark)"
850 (manufactured by DIC Corporation), "Epotohto (registered trademark)" YD-128 (manufactured
by Nippon Steel Chemical Co., Ltd.), and DER-331 and DER-332 (both manufactured by
The Dow Chemical Company).
[0033] Commercial products of bisphenol F-type epoxy resin include "jER (registered trademark)"
806, "jER (registered trademark)" 807, and "jER (registered trademark)" 1750 (all
manufactured by Mitsubishi Chemical Corporation), "EPICLON (registered trademark)"
830 (manufactured by DIC Corporation), and "Epotohto (registered trademark)" YD-170
(manufactured by Nippon Steel Chemical Co., Ltd.).
[0034] Commercial products of resorcinol type epoxy resin include "Denacol (registered trademark)"
EX-201 (manufactured by Nagase ChemteX Corporation).
[0035] Commercial products of biphenyl type epoxy resin include YX4000 (manufactured by
Mitsubishi Chemical Corporation).
[0036] Commercial products of urethane modified epoxy resin include AER4152 (manufactured
by Asahi Kasei E-materials Corp.).
[0037] Commercial products of hydantoin-type epoxy resin include AY238 (manufactured by
Huntsman Advanced Materials Gmbh).
[0038] A polyfunctional epoxy resin that is used as an epoxy resin except for a glycidyl
amine type, is described below.
[0039] Commercial products of isocyanurate-type epoxy resin include TEPIC-P (manufactured
by Nissan Chemical Industries, Ltd.).
[0040] Commercial products of tris-hydroxyphenyl methane-type epoxy resin include Tactix742
(manufactured by Huntsman Advanced Materials Gmbh).
[0041] Commercial products of tetraphenylol ethane-type epoxy resin include "jER (registered
trademark)" 1031 S (manufactured by Mitsubishi Chemical Corporation).
[0042] Commercial products of phenol novolac-type epoxy resin include DEN431and DEN438 (both
manufactured by The Dow Chemical Company) and "jER (registered trademark)" 152 (manufactured
by Mitsubishi Chemical Corporation).
[0043] Commercial products of orthocresol novolac-type epoxy resin include EOCN-1020 (manufactured
by Nippon Kayaku Co., Ltd.) and "EPICLON (registered trademark)" N-660 (manufactured
by DIC Corporation).
[0044] Commercial products of phenol aralkyl-type epoxy resin include NC-3000 (manufactured
by Nippon Kayaku Co., Ltd.).
[0045] Commercial products of dicyclopentadiene-type epoxy resin include "EPICLON (registered
trademark)" HP7200 (manufactured by DIC Corporation).
[0046] For the present invention, furthermore, a monofunctional epoxy resin can also be
used in order to a cured resin with an improved balance between the elastic modulus
and the elongation percentage. Commercial products of monofunctional epoxy resin include
"Denacol (registered trademark)" Ex-731 (glycidylphthalimide, manufactured by Nagase
ChemteX Corporation), OPP-G (o-phenyl phenyl glycidyl ether, manufactured by Sanko
Co., Ltd.), Ex-141 (phenyl glycidyl ether, manufactured by Nagase ChemteX Corporation),
and Ex-146 (tert-butyl phenyl glycidyl ether, manufactured by Nagase ChemteX Corporation).
[0047] Resin particles [B] to be used for the present invention, which is insoluble in epoxy
resins, must meet conditions (b1) to (b3) listed below:
(b1) the particles have a diameter distribution index of 1.0 to 1.8,
(b2) the particles have a sphericity of 90 or more, and
(b3) the particles have a glass transition temperature of 80 to 180°C.
[0048] Here, being insoluble in epoxy resins means that when an epoxy resin containing dispersed
resin particles are heat-cured, the resin particles substantially do not dissolve
in the epoxy resin, and that in observations by, for instance, transmission electron
microscopy, particles in the cured epoxy resin do not suffer from substantial shrinkage
from their original size and have clearly defined interfaces with the matrix resin.
[0049] Resin particles [B] used for the present invention should have a particle diameter
distribution index of 1.0 to 1.8, preferably 1.1 to 1.5. Such a relatively narrow
particle diameter distribution ensures that when prepregs produced by combining reinforcement
fibers with an epoxy resin composition containing dispersed resin particles are stacked
and heat-cured to form a fiber-reinforced composite material, resin particles will
not penetrate into the reinforcement fiber layers or regions with an excessive interlayer
thickness will not take place due to the existence of some bulky particles, leading
to a fiber-reinforced composite material with a uniform interlayer thickness. If the
particle diameter distribution index exceeds 1.8, some fine resin particles can penetrate
into the reinforcement fiber layers to cause a decrease in interlaminar toughness
and compressive strength under heat and humidity conditions, and the resulting uneven
interlayer thickness will lead to a material suffering from large variations in these
characteristics.
[0050] The particle diameter distribution index can be calculated by the following numeric
conversion equation using a particle diameter value determined by the method described
later.
[0051] 
[0052] Here, Di, n, Dn, Dv, and PDI denote the particle diameter of a particular particle,
number of measurements (100), number average particle diameter, volume average particle
diameter, and particle diameter distribution index, respectively.
[0053] Resin particles [B] used for the present invention should have a sphericity of 90
or more, preferably 92 or more, more preferably 96 or more, and most preferably 98
or more. Such a sphericity allows the epoxy resin composition containing these dispersed
resin particles to be low in viscosity, accordingly making it possible to increase
the content of the resin particles. If the sphericity is less than 90, the epoxy resin
composition will have a high viscosity and this limits the content of the resin particles,
leading to a material with poor interlaminar toughness.
[0054] The sphericity is determined by observing particles by scanning electronic microscopy,
measuring their major and minor axes, and calculating the sphericity by the following
numeric conversion equation from the average of measurements for randomly selected
30 particles.
[0055] 
[0056] Resin particles [B] used for the present invention should have a glass transition
temperature in the range of 80 to 180°C, more preferably 100 to 160°C , and still
more preferably 130 to 155°C. Such a relatively high glass transition temperature
ensures that resin particles will not suffer from deformation during heat-curing and
that a stable interlayer thickness will be achieved, making it possible to obtain
a fiber-reinforced composite material that has high interlaminar toughness and maintains
a compressive strength stably under heat and humidity conditions. If the glass transition
temperature is less than 80°C, the resulting adequate fiber-reinforced composite material
will fail to have a well-balanced combination of an interlaminar toughness and a compressive
strength under heat and humidity conditions. If the glass transition temperature is
more than 180°C, on the other hand, the resin particles themselves will tend to be
low in toughness and sufficient interface adhesion will not be achieved between the
resin particles and the matrix resin, resulting in a fiber-reinforced composite material
with poor interlaminar toughness.
[0057] The aforementioned glass transition temperature is determined by using differential
scanning calorimetry (DSC) as follows: a specimen is heated at a heating rate of 20°C/min
from 30°C to a temperature 30°C or more higher than an expected glass transition temperature,
maintained at the temperature for 1 min, once cooled at a cooling rate of 20°C/min
down to 0°C, maintained at the temperature for 1 min, and then heated again at a heating
rate of 20°C/min while observing the glass transition temperature (Tg).
[0058] If resin particles [B] insoluble in epoxy resins further meet the aforementioned
conditions from (b1) to (b3) simultaneously, the resin particles will fill a less
proportion of the interlayer regions between the fiber layers. Accordingly, a fiber-reinforced
composite material with a very large interlayer thickness between fiber layers can
be obtained even if the quantity of the resin particles existing in the interlayer
regions is not increased, and as a result, the mode II interlaminar toughness will
become unprecedentedly high. The interlayer thickness is preferably in the range of
25 to 40 µm, more preferably in the range of 27 to 37 µm. The interlayer thickness
can be measured by, for instance, the following procedure. A specimen of a fiber-reinforced
composite material is cut in a direction perpendicular to the carbon fibers, and the
cross section is polished and photographed with an optical microscope at a magnification
of 200 or more. In an appropriately-selected region between fiber layers in the photograph,
a line parallel to the carbon fiber layers is drawn so that it represents a carbon
fiber volume content of 50%, and it is assumed to be a boundary line between the internal
region of the fiber layer and the interlayer region between the fiber layers. A boundary
line averaged over a length of 100 µm is drawn, and the distance between them is assumed
to represent the interlayer thickness.
[0059] Resin particles [B] used for the present invention preferably has an average particle
diameter in the range of 8 to 35 µm, more preferably in the range of 10 to 30 µm.
An average particle diameter in this range ensures that when prepregs produced by
combining reinforcement fibers with an epoxy resin composition containing dispersed
resin particles are stacked and heat-cured to form a fiber-reinforced composite material,
resin particles will not penetrate into the reinforcement fiber layers or regions
with an excessive interlayer thickness will not result from the existence of some
bulky particles, leading to a fiber-reinforced composite material with a uniform interlayer
thickness. Accordingly, this ensures a stably high interlaminar toughness.
[0060] There are no specific limitations on the resin species used as resin particles [B]
for the present invention, and it may be either a thermoplastic resin or thermosetting
resin having a glass transition temperature in the range of 80°C to 180°C.
[0061] Specifically, usable thermoplastic resins include vinyl polymer, polyester, polyamide,
polyarylene ether, polyarylene sulfide, polyethersulfone, polysulfone, polyether ketone,
polyether ether ketone, polyurethane, polycarbonate, polyamide-imide, polyimide, polyetherimide,
polyacetal, silicone, and copolymers thereof.
[0062] Specifically, usable thermosetting resins include epoxy resin, benzoxazine resin,
vinyl ester resin, unsaturated polyester resin, urethane resin, phenol resin, melamine
resin, maleimide resin, cyanate ester resin, and urea resin.
[0063] The resins given above can be used singly or in combination.
[0064] Of these, polyamide, which is a thermoplastic resin, is preferred because of its
high elongation percentage, toughness, and adhesiveness with matrix resins. Examples
of polyamide include polyamide compounds that can be produced through condensation
polymerization of lactams having a 3- or more-membered ring, polymerizable aminocarboxylic
acids, dibasic acids, diamines, salts thereof, and mixtures thereof.
[0065] Specifically, they include polyhexamethylene terephthalamide (nylon 6T), polynonane
terephthalamide (nylon 9T), poly-m-xylene adipamide (nylon MXD), copolymers of 3,3'-dimethyl-4,4'-diaminodicyclohexyl
methane, isophthalic acid, and 12-aminododecanoic acid (for instance, "Grilamid (registered
trademark)" TR55, manufactured by Emser Werke, Inc.), copolymers of 3,3'-dimethyl-4,4'-diaminodicyclohexyl
methane and dodeca diacid (for instance, "Grilamid (registered trademark)" TR90, manufactured
by Emser Werke, Inc.), mixtures of a copolymer of 3,3'-dimethyl-4,4'-diaminodicyclohexyl
methane, isophthalic acid, and 12-aminododecanoic acid, and a copolymer of 3,3'-dimethyl-4,4'-diaminodicyclohexyl
methane and dodeca diacid (for instance, "Grilamid (registered trademark)" TR70LX,
manufactured by Emser Werke, Inc.), and copolymers of 4,4'-diaminodicyclohexyl methane
and dodeca diacid (for instance, "TROGAMID (registered trademark)" CX7323, manufactured
by Degussa AG).
[0066] In particular, a polyamide compound having a chemical structure as represented by
general formula (1) is preferred because when processed into a fiber-reinforced composite
material, it can provide a fiber-reinforced composite material having a high wet heat
resistance and solvent resistance as well as a high impact resistance and interlaminar
toughness.
[0067]

[0068] (In the formula, R
1 and R
2 represent a hydrogen atom, an alkyl group containing 1 to 8 carbon atoms, or a halogen
atom, and may be identical to or different from each other. In the formula, R
3 represents a methylene group containing 1 to 20 carbon atoms, or a phenylene group).
[0069] Such polyamide compounds include copolymers of 3,3'-dimethyl-4,4'-diaminodicyclohexyl
methane, isophthalic acid, and 12-aminododecanoic acid (for instance, "Grilamid (registered
trademark)" TR55, manufactured by Emser Werke, Inc.), copolymers of 3,3'-dimethyl-4,4'-diaminodicyclohexyl
methane and dodeca diacid (for instance, "Grilamid (registered trademark)" TR90, manufactured
by Emser Werke, Inc.), mixtures of a copolymer of 3,3'-dimethyl-4,4'-diaminodicyclohexyl
methane, isophthalic acid, and 12-aminododecanoic acid, and a copolymer of 3,3'-dimethyl-4,4'-diaminodicyclohexyl
methane and dodeca diacid (for instance, "Grilamid (registered trademark)" TR70LX,
manufactured by Emser Werke, Inc.), and copolymers of 4,4'-diaminodicyclohexyl methane
and dodeca diacid (for instance, "TROGAMID (registered trademark)" CX7323, manufactured
by Degussa AG).
[0070] In general formula (1), furthermore, R
3 more preferably represents a methylene group containing 1 to 20 carbon atoms. Such
polyamide compounds include a copolymer of 3,3'-dimethyl-4,4'-diaminodicyclohexyl
methane and dodeca diacid (for instance, "Grilamid (registered trademark)" TR90, manufactured
by Emser Werke, Inc.), and a copolymer of 4,4'-diaminodicyclohexyl methane and dodeca
diacid (for instance, "TROGAMID (registered trademark)" CX7323, manufactured by Degussa
AG).
[0071] The epoxy resin composition for fiber-reinforced composite material production according
to the present invention is required to contain at least one elastomer component,
[C], selected from the group consisting of rubber particles and block copolymers containing
a block with a glass transition temperature of 20°C or less. Such an elastomer component
[C] is added with the aim of forming a fine elastomer phase in a cured epoxy matrix
phase. Accordingly, a plane strain state caused by a mode I stress load applied to
a cured resin can be eliminated by destruction of the elastomer phase and formation
of gaps (cavitation) and plastic deformation of the epoxy matrix phase is induced.
As a result, a large energy absorption is caused, leading to a fiber-reinforced composite
material with an improved mode I interlaminar toughness. If such an elastomer component
[C] is at least one selected from the group consisting of core-shell rubber particles
and block copolymers containing a block with a glass transition temperature of 20°C
or less, a fine elastomer phase can be introduced while minimizing the compatibility
of the elastomer component with the epoxy resin, making it possible to form a fiber-reinforced
composite material with an improved mode I interlaminar toughness while previnting
a decrease of the heat resistance and elastic modulus.
[0072] In particular, if such an elastomer component [C] is used in combination with the
aforementioned resin particles [B], both the mode I interlaminar toughness and the
mode II interlaminar toughness are achieved at high levels through the mechanism described
below.
[0073] Specifically, a fiber-reinforced composite material containing the aforementioned
resin particles [B] in regions between fiber layers will have a large interlayer thickness,
leading to an improved mode II interlaminar toughness. regions between fiber layers
will contain an increased amount of the matrix resin, and as a result, when cracking
proceeds in interlayer regions, the matrix resin will absorb an increased amount of
energy, allowing elastomer component [C] to serve more effectively in improving the
mode I interlaminar toughness.
[0074] There are no specific limitations on the chemical structure, molecular weight, etc.
of the block copolymers containing a block with a glass transition temperature of
20°C or less, but it is preferable that the block with a glass transition temperature
of 20°C or less is not compatible with epoxy resins and that the block copolymers
also contain a block that is compatible with epoxy resins.
[0075] From the viewpoint of handleability etc., it is preferable that the aforementioned
rubber particles be crosslinked rubber particles or core-shell rubber particles consisting
of crosslinked rubber particles and a heterogeneous polymer graft-polymerized to their
surfaces. These rubber particles preferably have a primary particle diameter in the
range of 50 to 300 nm, particularly preferably 80 to 200 nm. It is also preferable
that these rubber particles have high affinity with the epoxy resin used and that
they do not undergo secondary coagulation during resin preparation, molding, or curing.
[0076] Commercial products of the crosslinked rubber particles include FX501P (manufactured
by Japan Synthetic Rubber Co., Ltd.), which is formed of a crosslinked, carboxyl modified
butadiene-acrylonitrile copolymer, and CX-MN series (manufactured by Nippon Shokubai
Co., Ltd.) and YR-500 series (manufactured by Nippon Steel Chemical Co., Ltd.), which
are formed of fine acrylic rubber particles.
[0077] Commercial products of the core shell rubber particles include, for instance, "Paraloid
(registered trademark)" EXL-2655 (manufactured by Kureha Corporation), which is formed
of a butadiene-alkyl methacrylate-styrene copolymerization, "Stafiloid (registered
trademark)" AC-3355 and TR-2122 (manufactured by Takeda Pharmaceutical Company Limited),
which is formed of a acrylate-methacrylate copolymer, "PARALOID (registered trademark)
EXL-2611" and EXL-3387 (Rohm and Haas Company), which is formed of a butyl acrylate-methyl
methacrylate copolymerization, and "Kane Ace (registered trademark)" MX series (Kaneka
Corporation).
[0078] It is also preferable that elastomer component [C] be at least one block copolymer
(hereinafter, occasionally referred to simply as block copolymer) selected from the
group consisting of copolymers having a structure of S-B-M, B-M, or M-B-M. This serves
to produce a fiber-reinforced composite material that has a largely improved mode
I interlaminar toughness while maintaining high heat resistance as well as high mechanical
strength under severe use conditions such as low temperature.
[0079] Here, each of the aforementioned blocks represented as S, B, and M is connected to
an adjacent one via a covalent bond, or via an intermediary molecule that is connected
to the block via a covalent bond and connected to the adjacent one via another covalent
bond.
[0080] Block M contains a homopolymer of polymethyl methacrylate or a copolymer in which
methyl methacrylate accounts for at least 50 wt%.
[0081] Block B is incompatible with block M and has a glass transition temperature Tg (hereinafter,
occasionally referred to simply as Tg) of 20°C or less.
[0082] Regardless of whether block B is produced from an epoxy resin composition or a single
block copolymer, its glass transition temperature Tg can be measured by DMA using
ARES (manufactured from TA Instruments), a dynamic viscoelasticity measuring device.
Specifically, a plate-like specimen of 1 × 2.5 × 34 mm is subjected to DMA while applying
periodic traction at 1 Hz in the temperature range of -60 to 250°C, and the value
of tan δ is assumed to represent its glass transition temperature Tg. Here, specimens
are prepared as follows. In the case where an epoxy resin composition is used, an
uncured resin composition is deaerated in a vacuum and then cured for 2 hours at a
temperature of 130°C in a mold set to a thickness of 1 mm using a "Teflon (registered
trademark)" spacer with a thickness of 1 mm to produce a void-free plate-like cured
material. In the case of a single block copolymer, a void-free plate can be produced
similarly by using a twin screw extruder. Thsese plates are cut to the aforementioned
size using a diamond cutter to provide specimens for evaluation.
[0083] Block S is incompatible with blocks B and M and has a glass transition temperature
Tg that is higher than that of block B.
[0084] From the viewpoint of improvement in toughness, furthermore, any of blocks S, B,
and M in an S-B-M type block copolymer or either block B and M of a B-M or M-B-M type
block copolymer be compatible with epoxy resins.
[0085] From the viewpoint of mechanical characteristics and adaptability to composite preparation
processes, the content of elastomer component [C] is preferably in the range of 2
to 15 parts by mass, more preferably 3 to 10 parts by mass, still more preferably
4 to 8 parts by mass, relative to 100 parts by mass, or the total amount, of the epoxy
resin in the epoxy resin composition. If the content is less than 2 parts by mass,
the resulting cured material will have a decreased toughness and plastic deformability,
leading to a fiber-reinforced composite material with a decreased interlaminar toughness.
If the content is more than 15 parts by mass, the resulting cured material will have
a significantly decreased elastic modulus, leading to a fiber-reinforced composite
material with a decreased compressive strength in the fiber direction. In addition,
adequate resin flow will not take place at the molding temperature, often resulting
in a fiber-reinforced composite material containing voids.
[0086] Introduction, as a copolymerization component, of a monomer other than methyl methacrylate
into the aforementioned block M has been practiced favorably from the viewpoint of
maintaining compatibility with epoxy resins and providing a cured material with various
controlled characteristics. There are no specific limitations on the monomeric components
for copolymerization, and suitable ones may be selected appropriately. To ensure compatibility
epoxy resins with a high SP value, however, the use of monomers with an SP value higher
than that of methyl methacrylate, water-soluble monomers in particular, has been preferred.
Among others, acrylamide derivatives can be used effectively, and the use of dimethyl
acrylamide is particularly effective. Furthermore, reactive monomers can also be used.
[0087] Here, the SP value means the generally known solubility parameter, which represents
the solubility and compatibility. There are some methods that calculate the SP value
from heat of evaporation or others that estimate the SP value from molecular structures.
Here, SP values calculated molecular structures according to Fedors' method described
in
Polym. Eng. Sci., 14(2), 147-154 (1974) should be adopted, and they should be represented in (cal/cm
3)
1/2.
[0088] A reactive monomer means a monomer having a functional group that can react with
an oxirane group in an epoxy molecule or a functional group in a curing agent. For
instance, useful examples include, but not limited to, monomers having reactive functional
groups such as oxirane group, amine group, or carboxyl group. Useful reactive monomers
include (meth)acrylic acid (in the present Description, methacrylic acid and acrylic
acid are collectively referred to as (meth)acrylic acid) and monomers that can form
(meth)acrylic acid through hydrolysis. The use of a reactive monomer is preferred
because it ensures Improvement in the compatibility with epoxy resins and adhesion
at the interface between epoxy resin and a block copolymer.
[0089] Other monomers that can serve to form block M include glycidyl methacrylate and tert-butyl
methacrylate, but it is preferable that at least 60% of block M is accounted for by
syndiotactic PMMA (polymethyl methacrylate).
[0090] The glass transition temperature Tg of block B is 20°C or less, preferably 0°C or
less, and more preferably -40°C or less. The glass transition temperature Tg should
be as low as possible from the viewpoint of toughness, but a Tg of less than -100°C
may cause some processability problems possibly resulting in a fiber-reinforced composite
material with a rough cut surface.
[0091] Block B is preferably an elastomer block, and it is preferable that the monomer to
be used to synthesize such an elastomer block be a diene selected from the group consisting
of butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 2-phenyl-1,3-butadiene.
From the viewpoint of toughness, in particular, it should preferably be selected from
the group consisting of polybutadiene, polyisoprene, random copolymer thereof, partially
or entirely hydrogenated polydiene. Useful polybutadiene compounds include 1,2-polybutadiene
(Tg: about 0°C), but it is more preferable to use a polybutadiene with a lowest level
glass transition temperature Tg such as 1,4-polybutadiene (Tg: about -90°C). This
because the use of a low block B with a low glass transition temperature Tg is advantageous
from the viewpoint of impact resistance and toughness. Block B may be hydrogenated.
This hydrogenation may be effected by a common method.
[0092] Useful monomers to constitute block B also include alkyl (meth)acrylate. Specific
examples include ethyl acrylate (-24°C), butyl acrylate (-54°C), 2-ethylhexyl acrylate
(-85°C), hydroxyethyl acrylate (-15°C), and 2-ethylhexyl meta-acrylate (-10°C). Here,
the figure in parentheses following each acrylate compound name shows the Tg of block
B that is formed from the acrylate compound. Of these, the use of butyl acrylate is
preferable. These acrylate monomers are incompatible with the acrylate component in
block M in which methyl methacrylate accounts for at least 50 wt%.
[0093] Of these, a block formed from a polymer selected from the group consisting of 1,4-polybutadiene,
polybutyl acrylate, and poly (2-ethylhexyl acrylate) is preferred as block B.
[0094] If a triblock copolymer S-B-M is used as the block copolymer, block S should be incompatible
with blocks B and M, and its glass transition temperature Tg should be higher than
that of block B. The Tg or melting point of block S is preferably 23°C or more, more
preferably 50°C or more. Examples of block S include those formed from an aromatic
vinyl compound such as styrene, α-methyl styrene, or vinyl toluene and those formed
from alkyl acid with an alkyl chain with a carbon atom of 1 to 18 and/ or an alkyl
ester of methacrylic acid. Those formed from alkyl acid with an alkyl chain with a
carbon atom of 1 to 18 and/ or an alkyl ester of methacrylic acid are mutually incompatible
with block M in which methyl methacrylate accounts for at least 50 wt%.
[0095] If a triblock copolymer M-B-M is used as the block copolymer, the two blocks M in
the triblock copolymer M-B-M may be identical to or different from each other. They
may be formed from the same type of monomers but have different molecular weights.
[0096] If a triblock copolymer M-B-M and a diblock copolymer B-M are usd in combination
as the block copolymer, block M in the triblock copolymer M-B-M and block M in the
diblock copolymer B-M may be identical to or different from each other, and block
B in the triblock M-B-M and that in the diblock copolymer B-M may be identical to
or different from each other.
[0097] If a triblock copolymer M-B-M and a diblock copolymer B-M are usd in combination
as the block copolymer, block M in the triblock copolymer M-B-M and block M in the
diblock copolymer B-M may be identical to or different from each other, and block
B in the triblock M-B-M and that in the diblock copolymer B-M may be identical to
or different from each other.
[0099] Specific examples of triblock copolymer S-B-M include Nanostrength 123, Nanostrength
250, Nanostrength 012, Nanostrength E20, and Nanostrength E40, styrene-butadiene-methyl
methacrylate based copolymer products manufactured by Arkema K.K. Specific examples
of triblock copolymer M-B-M include methyl methacrylate-butyl acrylate-methyl methacrylate
based copolymer products such as Nanostrength M22 manufactured by Arkema K.K. and
Nanostrength M22N and Nanostrength SM4032XM10 which are produced by copolymerizing
a monomer having a high SP value with the aforementioned Nanostrength M22 manufactured
by Arkema K.K. In particular, Nanostrength M22N and SM4032XM10, which are copolymerized
with a monomer having a high SP value, are preferred because they can form fine phase-separated
structures to achieve high toughness.
[0100] When used, the epoxy resin composition for fiber-reinforced composite material production
according to the present invention contains an epoxy resin curing agent [D]. A curing
agent as described herein is a curing agent for the epoxy resin contained in the epoxy
resin composition according to the present invention, and it is a compound having
an active group that can react with the epoxy group. Specifically, examples of the
curing agent include, for instance dicyandiamide, aromatic polyamine, aminobenzoic
acid ester, various anhydrides, phenol novolac resin, cresol novolac resin, polyphenol
compound, imidazole derivatives, aliphatic amine, tetramethyl guanidine, thiourea
addition amine, methyl hexahydro phthalic anhydride, other carboxylic anhydrides,
carboxylic acid hydrazide, carboxylic acid amide, polymercaptan, boron trifluoride
ethyl amine complex, and other Lewis acid complexes.
[0101] The use of aromatic polyamine as the curing agent makes it possible to produce a
cured epoxy resin with high heat resistance. In particular, of the various aromatic
polyamine compounds, diaminodiphenyl sulfone and their derivatives and various isomers
are the most suitable curing agents to produce a cured epoxy resin with a high heat
resistance.
[0102] Furthermore, if a combination of dicyandiamide and a urea compound such as 3, 4-dichlorophenyl-1,
1-dimethylurea, or an imidazole is used as the curing agent, high heat resistance
and water resistance can be achieved even when curing is performed at a relatively
low temperature. The use of an anhydride to cure an epoxy resin provides a cured material
that has a lower water absorption percentage compared to curing with an amine compound.
Other curing agents include the above ones in latent forms such as microencapsulated
ones, which serve to provide prepregs with high storage stability that will not suffer
from significant changes particularly in tackiness and drape property even if left
to stand at room temperature.
[0103] The optimum content of a curing agent depends on the type of epoxy resin and curing
agent used. In the case of an aromatic amine curing agent, for instance, it is preferable
to add it so that it will be stoichiometrically equivalent. However, a resin with
a higher elastic modulus compared to the case of equivalency may be obtained when
using an epoxy resin and an aromatic amine curing agent in such a manner that the
ratio of the quantity of active hydrogen in the latter to the quantity of the epoxy
group in the former is about 0.7 to 0.9, and this is also a preferable embodiment.
These curing agents may be used singly or a plurality thereof may be used in combination.
[0104] Commercial products of aromatic polyamine curing agents include Seikacure S (manufactured
by Wakayama Seika Kogyo Co., Ltd.), MDA-220 (manufactured by Mitsui Chemicals, Inc.),
"jER Cure (registered trademark)" W (manufactured by Mitsubishi Chemical Corporation),
and 3,3'-DAS (manufactured by Mitsui Chemicals, Inc.), "Lonzacure (registered trademark)"
M-DEA (manufactured by Lonza), "Lonzacure (registered trademark)" M-DIPA (manufactured
by Lonza), "Lonzacure (registered trademark)" M-MIPA (manufactured by Lonza), and
"Lonzacure (registered trademark)" DETDA 80 (manufactured by Lonza).
[0105] A composition may contain these epoxy resins and curing agents, part of which may
be subjected to preliminary reaction in advance. In some cases, this method can serve
effectively for viscosity adjustment and storage stability improvement.
[0106] For the epoxy resin composition for fiber-reinforced composite material production
according to the present invention, it is preferable that the constituents (components)
other than resin particles [B] and epoxy resin curing agent [D] be first heated and
kneaded uniformly at a temperature of about 150 to 170°C and cooled to a temperature
of about 60°C, and then resin particles [B] and epoxy resin curing agent [D] are added,
followed by further kneading, although methods to be used to mix the components are
not limited to this.
[0107] The epoxy resin composition according to the present invention may contain a coupling
agent, thermosetting resin particles, thermoplastic resin soluble in epoxy resins,
or inorganic fillers such as silica gel, carbon black, clay, carbon nanotube, and
metal powder, unless they impair the effect of the invention.
[0108] The prepreg according to the present invention is produced by impregnating reinforcement
fibers with the aforementioned epoxy resin composition for fiber-reinforced composite
material production. Reinforcement fibers that can be used for the prepreg according
to the present invention include carbon fiber, glass fiber, aramid fiber, boron fiber,
PBO fiber, high-strength polyethylene fiber, alumina fiber, and silicon carbide fiber.
A plurality of these fibers may be used as a mixture. There are no specific limitations
on the form and way of alignment of the reinforcement fibers, and useful fiber structures
include, for instance, long fibers paralleled in one direction, single tow, woven
fabric, knit fabric, nonwoven fabric, mat, and braid.
[0109] With a high specific modulus and specific strength, carbon fibers can be used effectively,
particularly when it is necessary to produce lightweight or high-strength materials.
[0110] With respect to carbon fibers used preferably for the present invention, virtually
any type of carbon fibers can be adopted for specific uses, but it is preferable that
the carbon fibers used have a tensile modulus up to 400 GPa from the viewpoint of
interlaminar toughness and impact resistance. From the viewpoint of strength, carbon
fibers with a tensile strength of 4.4 to 6.5 GPa are used preferably because a composite
material with high rigidity and mechanical strength can be produced. Tensile elongation
is also an important factor, and it is preferable that the carbon fibers have a high
strength and a high elongation percentage of 1.7 to 2.3%. The most suitable carbon
fibers will simultaneously have various characteristics including a tensile modulus
of at least 230 GPa, tensile strength of at least 4.4 GPa, and tensile elongation
of at least 1.7%.
[0111] Commercial products of carbon fibers include "Torayca (registered trademark)" T800G-24K,
"Torayca (registered trademark)" T800S-24K, "Torayca (registered trademark)" T700G-24K,
"Torayca (registered trademark)" T300-3K, and "Torayca (registered trademark)" T700S-12K
(all manufactured by Toray Industries, Inc.).
[0112] With respect to the form of way of alignment of carbon fibers, long fibers paralleled
in one direction, woven fabric, or others may be selected appropriately, but if a
carbon fiber-reinforced composite material that is lightweight and relatively highly
durable is to be obtained, it is preferable to use carbon fibers in the form of long
fibers (fiber bundles) paralleled in one direction, woven fabric, or other continuous
fibers.
[0113] Carbon fiber bundles to be used for the present invention preferably have a monofilament
fineness of 0.2 to 2.0 dtex, more preferably 0.4 to 1.8 dtex. If the monofilament
fineness is less than 0.2 dtex, carbon fiber bundles may be damaged easily due to
contact with guide rollers during twining, and similar damage may take place during
an impregnation step for the resin composition. If the monofilament fineness is more
than 2.0 dtex, resin composition can fail to impregnate carbon fiber bundles sufficiently,
possibly resulting in a decrease in fatigue resistance.
[0114] The carbon fiber bundles to be used for the present invention preferably contain
2,500 to 50,000 filaments per fiber bundle. If the number of filaments is less than
2,500, fibers may be easily caused to meander, leading to a decrease in strength.
If the number of filaments is more than 50,000, resin impregnation may be difficult
during prepreg preparation or during molding. The number of filaments is more preferably
in the range of 2,800 to 40,000.
[0115] It is preferable that the prepreg according to the present invention be in the form
of carbon fiber impregnated with an epoxy resin composition for fiber-reinforced composite
material production, and the mass fraction of carbon fibers in the prepreg is preferably
40 to 90 mass%, more preferably 50 to 80 mass%. If the mass fraction of carbon fibers
is too low, the resulting composite material will be too heavy and the advantage of
the fiber-reinforced composite material having high specific strength and specific
modulus will be impaired in some cases, while if the mass fraction of carbon fibers
is too high, impregnation with the resin composition will not performed sufficiently
and the resulting composite material will suffer from many voids, possibly leading
to large deterioration in mechanical characteristics.
[0116] The prepreg according to the present invention preferably has a structure in which
a particle-rich layer, that is, a layer in which localized existence of the aforementioned
resin particles [B] is clearly confirmed in observed cross sections (hereinafter,
occasionally referred to as particle layer), is formed near the surface of the prepreg.
[0117] If a carbon fiber-reinforced composite material is produced by stacking prepregs
and curing the epoxy resin, this structure allows a resin layer to be formed easily
between prepreg layers, i.e., composite material layers. Accordingly, strong adhesion
and contact will be achieved between composite material layers and the resulting carbon
fiber-reinforced composite material will have high-level interlaminar toughness and
impact resistance.
[0118] From this viewpoint, the aforementioned particle layer preferably exists within the
depth range of 20%, more preferably 10%, of the total thickness (100%) of the prepreg,
measured from the surface of the prepreg in the thickness direction, with the measurement
started from the surface of the prepreg. Furthermore, a particle layer may exist only
at one side, but cautions are necessary because the prepreg will have two different
sides. If interlayer regions containing particles and those free of particles coexist
as a result of stacking of prepregs in an inappropriate way by mistake, the resulting
composite material will have poor interlaminar toughness. It is preferable that particle
layers exist at both sides of the prepreg, allowing the prepreg to have two identical
sides and making the stacking operation easy.
[0119] Furthermore, the proportion of thermoplastic resin particles existing in the particle
layers is preferably 90 to 100 mass%, more preferably 95 to 100 mass%, of the total
quantity, or 100 mass%, of thermoplastic resin particles existing in the prepreg.
[0120] This proportion of existing particles can be evaluated by, for instance, the undermentioned
method. Specifically, a prepreg is interposed between two polytetrafluoroethylene
resin plates with smooth surfaces and brought into close contact, then the temperature
is increased gradually for 7 days up to a curing temperature to ensure gelation and
curing, thus producing a plate-like cured prepreg. After the curing step is completed,
the cured prepreg is cut in a direction perpendicular to the contact surfaces and
the cross section is polished and then photographed with an optical microscope, followed
by drawing two lines, each being parallel to a surface of the prepreg and located
at a depth equal to 20% of the thickness from the surface. Then, the total area of
the particles existing between each surface of the prepreg and each of the lines drawn
above and the total area of the particles existing across the entire thickness of
the prepreg are determined, followed by calculating the proportion of the number of
particles existing in the regions of 20% depth from the prepreg surfaces to the total
number of particles existing across the entire (100%) thickness of the prepreg. Here,
the total area of the particles is determined by cutting the particle portions out
of a cross-sectional photograph and converting their mass. The particles may be dyed
if it is difficult to identify the particle portions dispersed in the cross-sectional
photograph.
[0121] The prepreg according to the present invention can be produced by applying methods
as disclosed in Japanese Unexamined patent Publication (Kokai) No.
HEI-1-26651, Japanese Unexamined patent Publication (Kokai) No.
SHO-63-170427, or Japanese Unexamined patent Publication (Kokai) No.
SHO-63-170428. Specifically, the prepreg according to the present invention can be produced by
a method in which the surface of a primary prepreg consisting of carbon fibers and
an epoxy resin, i.e., matrix resin, is coated with thermoplastic resin particles,
which are simply in the form of particles, a method in which a mixture these particles
mixed uniform in an epoxy resin, i.e., matrix resin, is prepared and used to impregnate
carbon fiber, and during this impregnation process, reinforcement fibers are located
so that it acts to prevent the penetration of these particles to ensure localized
existence of particles in the prepreg's surface regions, and a method in which a primary
prepreg is prepared in advance by impregnating carbon fibers with an epoxy resin,
and a thermosetting resin film containing these particles at a high concentration
is bonded on the surface of the primary prepreg. The uniform existence of thermoplastic
resin particles in the region of 20% depth of the thickness of the prepreg serves
to produce a prepreg for fiber composite material production having high interlaminar
toughness.
[0122] The prepreg according to the present invention can be produced favorably by some
different methods including a wet method in which the epoxy resin composition according
to the present invention is dissolved in a solvent such as methyl ethyl ketone and
methanol to produce a solution with a decreased viscosity, and then used to impregnate
reinforcement fibers and a hot melt method in which the epoxy resin composition is
heated to decrease its viscosity and then used to impregnate reinforcement fibers.
[0123] In the wet method, reinforcement fibers are immersed in a solution of the epoxy resin
composition and then pulled out, and the solvent is evaporated using a tool such as
oven to provide a prepreg.
[0124] In a hot melt method, an epoxy resin composition, with its viscosity decreased by
heating, is used directly to impregnate reinforcement fibers. Alternatively, resin
films are prepared by coating release paper or the like with an epoxy resin composition
and the resin films are used to cover either or both sides of reinforcement fibers
and pressed under heat so that the epoxy resin composition is transferred to them
for impregnation, thereby producing a prepreg. This hot melt method is preferred because
virtually no solvent will remain in the prepreg.
[0125] The fiber-reinforced composite material according to the present invention can be
produced by, for instance, stacking a plurality of prepregs prepared by a method as
described above and heat and pressure are applied to the resulting layered body to
heat-cure the epoxy resin.
[0126] The application of heat and pressure is carried out by using such methods as press
molding, autoclave molding, bagging molding, wrapping tape molding, and internal pressure
molding. In particular, wrapping tape molding and internal pressure molding have been
preferred for production of molded sports goods.
[0127] In the wrapping tape molding method, a core bar such as mandrel is wound with a prepreg
to produce a tube of fiber-reinforced composite material, and this method is suitable
for manufacturing rod-like products including golf club shaft and fishing rod. More
specifically, a mandrel is wound with a prepreg and further wound with a wrapping
tape of thermoplastic resin film to cover the prepreg so that the prepreg is secured
and pressed, followed by heating and curing the epoxy resin in an oven and removing
the core bar to provide a tubular material.
[0128] In the internal pressure molding method, a preform formed of an internal pressure
applying body such as a tube of thermoplastic resin wound with a prepreg is fixed
in a mold, and high pressure gas is introduced into the internal pressure applying
body to apply pressure and heat the mold simultaneously to produce a tube-like body.
The internal pressure molding method has been preferred particularly for the molding
of articles of a complicated shape such as golf club shaft, bat, and rackets for tennis
and badminton.
[0129] As an example, the carbon fiber-reinforced composite material according to the invention
can be produced by stacking sheets of the aforementioned prepreg according to the
invention into a required shape and subsequently pressed under heat to cure the epoxy
resin.
[0130] In another process, the fiber-reinforced composite material according to the invention
can be produced from the aforementioned epoxy resin composition without using a prepreg.
[0131] This can be effected by, for instance, impregnating reinforcement fibers directly
with the epoxy resin composition according to the invention, and subsequently heat-curing
it, and available methods include hand lay-up, filament winding, pultrusion, resin
film infusion, resin injection molding, and resin transfer molding.
Examples
[0132] The epoxy resin composition according to the invention as well as a prepreg and a
fiber-reinforced composite material produced therefrom are described in detail below
with reference to Examples. Described below are the resin materials used in Examples
and the preparation and evaluation methods used for prepregs and fiber-reinforced
composite materials. Preparation and evaluation of prepregs in Examples were performed
in an atmosphere with a temperature of 25° C±2° C and relative humidity of 50% unless
otherwise specified.
<Carbon Fiber (Reinforcement Fiber)>
[0133]
○ "Torayca (registered trademark)" T800G-24K-31E (carbon fiber with 24,000 filaments/bundle,
tensile strength of 5.9 GPa, tensile modulus of 294 GPa, tensile elongation of 2.0%,
manufactured by Toray Industries, Inc.).
<Epoxy Resin [A]>
[0134]
○ ELM434 (tetraglycidyl diaminodiphenyl methane, manufactured by Sumitomo Chemical
Co., Ltd.)
○ "jER (registered trademark)" 630 (triglycidyl-p-aminophenol, manufactured by Mitsubishi
Chemical Corporation)
○ MY0600 (m-aminophenol type epoxy resin, epoxy equivalent 118, manufactured by Huntsman
Advanced Materials K.K.)
○ "jER (registered trademark)" 828 (bisphenol A type epoxy resin, manufactured by
Mitsubishi Chemical Corporation))
○ "EPICLON (registered trademark)" 830 (bisphenol F-type epoxy resin, manufactured
by DIC Corporation)
○ GOT (N-diglycidyl toluidine, manufactured by Nippon Kayaku Co., Ltd.)
○ GAN (N-diglycidyl aniline, manufactured by Nippon Kayaku Co., Ltd.)
○ "EPICLON (registered trademark)" HP7200H (epoxy resin containing dicyclopentadiene
backbone, manufactured by DIC Corporation)
<Elastomer component [C]>
[0135]
○ "Nanostrength (registered trademark)" M22N (M-B-M type block copolymer where B denotes
butyl acrylate (Tg: -54°C) and M denotes a random copolymer chain containing methyl
methacrylate and polar acrylic monomer, manufactured by Arkema K.K.)
○ "Nanostrength (registered trademark)" SM4032XM10 (M-B-M type block copolymer where
B denotes butyl acrylate (Tg: -54°C) and M denotes a random copolymer chain composed
of methyl methacrylate and carboxyl-containing acrylic monomer, manufactured by Arkema
K.K.)
○ "Kane Ace (registered trademark)" MX-416 (core-shell rubber particles of styrene-butadiene-methyl
methacrylate, average particle diameter 100 nm, manufactured by Kaneka Corporation).
Tetraglycidyl diaminodiphenyl methane based master batch with a concentration of 25
mass%. In the constituent lists for Examples and Comparative examples in Table 1,
the contents of rubber particles are given in parts by mass and the tetraglycidyl
diaminodiphenyl methane component in master batches is included in ELM434.
<Epoxy resin curing agent [D]>
[0136]
○ "Seikacure (registered trademark)" -S (4, 4'-diaminodiphenyl sulfone, manufactured
by Wakayama Seika Kogyo Co., Ltd.)
○ 3, 3'-DAS (3, 3'-diaminodiphenyl sulfone, manufactured by Mitsui Fine Chemical,
Inc.)
<Other components>
[0137]
○ "Sumikaexcel (registered trademark)" PES5003P (polyethersulfone, manufactured by
Sumitomo Chemical Co., Ltd.)
<Resin particles [B]>
[0138]
○ Particle 1 (particles produced from "Trogamid (registered trademark)" CX7323 used
as raw material, and having an average particle diameter of 19.5 µm, particle diameter
distribution index of 1.17, sphericity of 98, and Tg of 137°C)
(Production method for particle 1: by reference to International Publication WO 2009/142231)
[0139] In a 1,000 ml four-neck flask, 20 g of polyamide (weight average molecular weight
17, 000, "TROGAMID (registered trademark)" CX7323, manufactured by Degussa) used as
polymer A, 500 g formic acid used as an organic solvent, and 20 g of polyvinyl alcohol
(PVA 1000, manufactured by Wako Pure Chemical Industries, Ltd., SP value 32.8 (J/cm
3)
1/2) used as polymer B were heated at 80°C and stirred to ensure dissolution of the polymers.
After lowering the temperature of the system to 55°C, 500 g of ion-exchanged water,
which was used as poor solvent, started to be added through a water supply pump at
a rate of 0.5 g/min while maintaining an adequately stirred state and stirring the
solution at 900 rpm. The dripping rate was gradually increased as the addition was
continued, and the addition of the entire quantity was finished in 90 min. The solution
turned to white when 100 g of ion-exchanged water had been added. When a half quantity
of the ion-exchanged water had been added, the temperature of the solution was raised
to 60°C, and subsequently the remaining ion-exchanged water was poured. After finishing
the addition of the entire quantity, stirring was continued for additional 30 min.
The resulting suspension liquid was cooled to room temperature and filtered, followed
by washing with 500 g of ion-exchanged water and vacuum-drying at 80°C for 10 hours
to provide 11 g of a white solid material. The resulting powder was observed by scanning
electron microscopy and it was found to be fine particles of polyamide with an average
particle diameter of 19.5 µm, particle diameter distribution index of 1.17, and sphericity
of 98.
○ Particle 2 (Particles produced from "Grilamid (registered trademark)" TR90 used
as starting material and having an average particle diameter of 9.2 µm, particle diameter
distribution index of 1.46, sphericity of 96, and Tg of 152°C)
(Production method for particle 2: by reference to International Publication WO 2009/142231)
[0140] In a 1,000 ml four-neck flask, 2.1 g of amorphous polyamide ("Grilamid (registered
trademark)" TR90 manufactured by Emser Werke, Inc., weight average molecular weight
12,300) used as polymer A, 25.8 g of formic acid (manufactured by Wako Pure Chemical
Industries, Ltd.) used as organic solvent, and 2.1 g of polyvinyl alcohol ("Gohsenol
(registered trademark)" GM-14 manufactured by Nippon Synthetic Chemical Industry Co.,
Ltd. industry, weight average molecular weight 22,000, SP value 32.8 (J/cm
3)
1/2) used as polymer B were heated at 80°C and stirred to ensure dissolution of the polymers.
After lowering the temperature of the system back to room temperature, 60 g of ion-exchanged
water, which was used as poor solvent, started to be added through a water supply
pump at a rate of 0.05 g/min while stirring the solution at 900 rpm. The dripping
rate was gradually increased as the addition was continued, and the addition of the
entire quantity was finished in 90 min. The solution turned to white when 10 g of
ion-exchanged water had been added. When a half quantity of the ion-exchanged water
had been added, the temperature of the solution was raised to 60°C, and subsequently
the remaining ion-exchanged water was poured. After finishing the addition of the
entire quantity, stirring was continued for additional 30 min. The resulting suspension
liquid was cooled to room temperature and filtered, followed by washing with 50 g
of ion-exchanged water and vacuum-drying at 80°C for 10 hours to provide 2.0 g of
a white solid material. The resulting powder was observed by scanning electron microscopy
and it was found to be fine particles of polyamide with an average particle diameter
of 9.2 µm, particle diameter distribution index of 1.46, and sphericity of 96.
○ Particle 3 (Particles produced from "Grilamid (registered trademark)" TR90 used
as starting material and having an average particle diameter of 15.3 µm, particle
diameter distribution index of 1.77, sphericity of 92, and Tg of 152°C)
(Production method for particle 3: by reference to International Publication WO 2009/142231)
[0141] In a 1,000 ml four-neck flask, 2.1 g of amorphous polyamide ("Grilamid (registered
trademark") TR90 manufactured by Emser Werke, Inc., weight average molecular weight
12,300) used as polymer A, 25.8 g of formic acid (manufactured by Wako Pure Chemical
Industries, Ltd.) used as organic solvent, and 2.1 g of polyvinyl alcohol ("Gohsenol
(registered trademark)" GM-14 manufactured by Nippon Synthetic Chemical Industry Co.,
Ltd. industry, weight average molecular weight 22,000, SP value 32.8 (J/cm
3)
1/2) used as polymer B were heated at 80°C and stirred to ensure dissolution of the polymers.
After lowering the temperature of the system to 40°C, 60 g of ion-exchanged water,
which was used as poor solvent, started to be added through a water supply pump at
a rate of 0.05 g/min while stirring the solution at 900 rpm. The dripping rate was
gradually increased as the addition was continued, and the addition of the entire
quantity was finished in 90 min. The solution turned to white when 10 g of ion-exchanged
water had been added. When a half quantity of the ion-exchanged water had been added,
the temperature of the solution was raised to 60°C, and subsequently the remaining
ion-exchanged water was poured. After finishing the addition of the entire quantity,
stirring was continued for additional 30 min. The resulting suspension liquid was
cooled to room temperature and filtered, followed by washing with 50 g of ion-exchanged
water and vacuum-drying at 80°C for 10 hours to provide 2.0 g of a white solid material.
The resulting powder was observed by scanning electron microscopy and it was found
to be fine particles of polyamide with an average particle diameter of 15.3 µm, particle
diameter distribution index of 1.77, and sphericity of 92.
○ Particle 4 (Particles produced from "Grilamid (registered trademark)" TR55 used
as starting material and having an average particle diameter of 16.1 µm, particle
diameter distribution index of 1.20, sphericity of 95, and Tg of 160°C)
(Production method for particle 4: by reference to International Publication WO 2009/142231)
[0142] In a 1,000 ml four-neck flask, 2.5 g of amorphous polyamide ("Grilamid (registered
trademark)" TR55 manufactured by Emser Werke, Inc., weight average molecular weight
18, 000) used as polymer A, 42.5 g of N-methyl-2-pyrolidone used as organic solvent,
and 5 g of polyvinyl alcohol ("Gohsenol (registered trademark)" GL-05 manufactured
by Nippon Synthetic Chemical Industry Co., Ltd. industry) used as polymer B were heated
at 80°C and stirred to ensure dissolution of the polymers. After lowering the temperature
of the system back to room temperature, 50 g of ion-exchanged water, which was used
as poor solvent, was dropped through a water supply pump at a rate of 0.41 g/min while
stirring the solution at 450 rpm. The solution turned to white when 12 g of ion-exchanged
water had been added. After finishing the addition of the total quantity of water,
stirring was continued for 30 min, and the resulting suspension liquid was filtered,
followed by washing with 100 g of ion-exchanged water and vacuum-drying at 80°C for
10 hours to provide 2.2 g of a white solid material. The resulting powder was observed
by scanning electron microscopy and found to be fine particles of polyamide with an
average particle diameter of 16.1 µm, particle diameter distribution index of 1.20,
and sphericity of 95.
<Other resin particles>
[0143]
○ Particle 5 (particles produced from poly(2, 6-dimethyl phenylene ether) as raw material,
average particle diameter 8.6 µm, particle diameter distribution index 1.11, sphericity
97, Tg 215°C)
(Production method for particle 5: by reference to International Publication WO 2009/142231)
[0144] In a 1,000 ml four-neck flask, 2.5 g of 2.5 g of poly(2, 6-dimethyl phenylene ether)
(weight average molecular weight 55,000) used as polymer A, 45 g of N-methyl-2-pyrolidone
used as organic solvent, and 2.5 g of polyvinyl alcohol ("Gohsenol (registered trademark)"
GL-05 manufactured by Nippon Synthetic Chemical Industry Co., Ltd. industry) used
as polymer B were heated at 80°C and stirred to ensure dissolution of the polymers.
After lowering the temperature of the system back to room temperature, 50 g of ion-exchanged
water, which was used as poor solvent, was dropped through a water supply pump at
a rate of 0.41 g/min while stirring the solution at 450 rpm. The solution turned to
white when 12 g of ion-exchanged water had been added. After finishing the addition
of the total quantity of water, stirring was continued for 30 min, and the resulting
suspension liquid was filtered, followed by washing with 100 g of ion-exchanged water
and vacuum-drying at 80°C for 10 hours to provide 2.25 g of a white solid material.
The resulting powder was observed by scanning electron microscopy and found to be
fine particles of poly(2, 6-dimethyl phenylene ether) with an average particle diameter
of 8.6 µm, particle diameter distribution index of 1.11, and sphericity of 97.
○ Particle 6 (Particles produced from "Grilamid (registered trademark)" TR55 manufactured
by Emser Werke, Inc., used as starting material, and having an average particle diameter
of 18.0 µm, particle diameter distribution index of 1.52, sphericity of 85, and Tg
of 160°C)
(Production method for Particle 6)
[0145] First, 94 parts by weight of polyamide ("Grilamid (registered trademark)" TR-55 manufactured
by Emser Werke, Inc.), which contains 4,4'-diamino-3,3'-dimethyl dicyclohexyl methane
as essential component, 4 parts by weight of epoxy resin ("jER (registered trademark)"
828 manufactured by Japan Epoxy Resins Co., Ltd.), and 2 parts by weight of a curing
agent ("Tormide (registered trademark)" #296 manufactured by Fuji Kasei Kogyo Co.,
Ltd.) were added to a mixed solvent composed of 300 parts by weight of chloroform
and 100 parts by weight of methanol to provide a uniform solution. Then, using a spray
gun for painting, the solution was sprayed strongly against the liquid surface of
3,000 parts by weight of well-stirred n-hexane in order to separate out the solute.
The solid material thus separated was filtered out, washed well with n-hexane, vacuum-dried
at 100°C for 24 hours, and passed through sieves to remove particles with small diameters
and those with large diameters to obtain transparent polyamide particles with a relatively
small particle diameter distribution. The resulting powder was observed by scanning
electron microscopy and it was found to be fine particles of polyamide with an average
particle diameter of 18.0 µm, particle diameter distribution index of 1.52, and sphericity
of 85. ○ Particle 7 ("Toraypearl (registered trademark)" TN, manufactured by Toray
Industries, Inc., average particle diameter 13.0 µm, particle diameter distribution
index 2.10, sphericity 96, Tg 167°C)
○ Particle 8 ("Orgasol (registered trademark)" 1002D, manufactured by Arkema K.K.,
average particle diameter 20 µm, particle diameter distribution index 1.30, sphericity
97, Tg 53°C)
(1) Measurement of average particle diameter, particle diameter distribution index,
and sphericity of resin particles
[0146] The particle diameter of individual resin particles was measured by observing the
fine particles by scanning electron microscopy (JSM-6301NF scanning electron microscope
manufactured by JEOL Ltd.) at a magnification of 1,000. Here, if a particle is not
perfectly circular, its major axis was measured and used as its particle diameter.
[0147] To determine the average particle diameter, 100 particles in a photograph were randomly
selected and their diameters were measured, followed by calculating the arithmetic
average. The average particle diameter as referred to herein is the number average
particle diameter. The particle diameter distribution index was calculated by the
following numeric conversion equation using the diameters of individual particles
determined above.
[0148] 
[0149] Here, Di, n, Dn, Dv, and PDI denote the particle diameter of a particular particle,
number of measurements (100), number average particle diameter, volume average particle
diameter, and particle diameter distribution index, respectively.
[0150] The sphericity is determined by measuring the major and minor axes of randomly selected
30 particles in a photograph, and calculating the sphericity by the following equation
from the average of the measurements.
[0151] 
(2) Measurement of glass transition temperature (Tg) of resin particles
[0152] Using differential scanning calorimetry (DSC), resin particles are heated at a heating
rate of 20°C/min from 30°C to a temperature 30°C or more higher than an expected glass
transition temperature, maintained at the temperature for 1 min, once cooled at a
cooling rate of 20°C/min down to 0°C, maintained at the temperature for 1 min, and
then heated again at a heating rate of 20°C/min while observing the glass transition
temperature (Tg).
[0153] Specifically, in the stepwise changing portion of a resulting DSC curve, the glass
transition temperature was defined as the temperature at the point where the straight
line that is at the same distance in the vertical direction from the extensions of
the baselines intersects the curve that changes stepwise due to glass transition.
Here, a Model 2910 differential scanning calorimeter manufactured by TA Instruments
was used for the measurement.
(3) Preparation of epoxy resin composition
[0154] Predetermined amounts of a curing agent, curing accelerator, and non-particle components
were put in a kneader according to the compounding ratios specified in Table 1 and
heated to 160°C while kneading, followed by kneading at 160°C for 1 hour to provide
a transparent viscous liquid. After cooling to 80°C while kneading, curing agent,
predetermined amounts of a curing accelerator and particles were added and further
kneaded to provide an epoxy resin composition.
(4) Measurement of bending elastic modulus of cured resin
[0155] The resin composition prepared in section (3) was deaerated in a vacuum and injected
in a mold which was set up so that the thickness would be 2 mm by means of a 2 mm
thick "Teflon (trademark)" spacer. Curing was performed at a temperature of 180°C
for 2 hours to provide a cured resin with a thickness of 2 mm. Then, the resulting
cured resin plate was cut to prepare a test piece with a width of 10 mm and length
of 60 mm, and it was subjected to three-point bending test with a span of 32 mm, followed
by calculation of the bending elastic modulus according to JIS K7171-1994.
(5) Measurement of toughness (KIC) of cured resin
[0156] The resin composition prepared in section (3) was deaerated in a vacuum and injected
in a mold which was set up so that the thickness would be 6 mm by means of a 6 mm
thick "Teflon (trademark)" spacer, followed by curing at a temperature of 180°C for
2 hours to provide a cured resin with a thickness of 6 mm. This a cured resin was
cut to prepare a test piece with a size of 12.7 × 150 mm. Using an Instron type universal
tester (manufactured by Instron Corporation), test piece was processed and tested
according to ASTM D5045 (1999). An initial precrack was introduced in the test piece
by putting the edge of a blade cooled to the liquid nitrogen temperature on the test
piece and giving an impact to the razor using a hammer. The toughness of a cured resin
as referred to herein means the critical stress intensity factor for mode I (opening-mode)
deformation.
(6) Preparation of prepreg
[0157] An epoxy resin composition was spread over a piece of release paper with a knife
coater to prepare a resin film. Then, carbon fibers of "Torayca (registered trademark)"
T800G-24K-31E manufactured by Toray Industries, Inc. was paralleled in one direction
to form a sheet, and two resin films were used to cover both sides of the carbon fiber
sheet and pressed under heat to impregnate the carbon fibers with the resin to provide
a unidirectional prepreg with a carbon fiber basis weight of 190 g/m
2 and matrix resin weight fraction of 35.5%. In doing this, two-step impregnation was
carried out to produce a prepreg in which resin particles are extremely localized
near the surface.
[0158] To provide a resin film for primary prepreg production, an epoxy resin composition
containing no resin particles and having the same constitution as specified in Table
1 except for resin particles was prepared by the same procedure as specified in section
(3). This epoxy resin composition was spread over a piece of release paper with a
knife coater to provide a resin film with a basis weight of 30 g/m
2, which corresponds to 60 mass% of the normal value. Then, carbon fibers of "Torayca
(registered trademark)" T800G-24K-31E manufactured by Toray Industries, Inc. was paralleled
in one direction to form a sheet, and two resin films were used to cover both sides
of the carbon fiber sheet and pressed under heat using heating rollers at a temperature
of 100°C and an air pressure of 1 atm to impregnate the carbon fibers with the resin
to provide a primary prepreg.
[0159] To provide a resin film for two-step impregnation, an epoxy resin composition containing
resin particles at a proportion (in parts by mass) as given in Table 2 relative to
the total epoxy resin component (100 parts by mass) and having the same constitution
as specified in Table 1 for the components other than the resin particles was prepared
by the same procedure as specified in section (3). This epoxy resin composition was
spread over a piece of release paper with a knife coater to provide a resin film with
a basis weight of 20 g/m
2, which corresponds to 40 mass% of the normal value. Such films were used to sandwich
the primary prepreg and pressed under heat using heating rollers at a temperature
of 80°C and an air pressure of 1 atm to provide a prepreg in which resin particles
are extremely localized near the surface. The use of this two-step impregnation process
serves to produce a prepreg in which resin particles are extremely localized near
the surface although as a whole the epoxy resin composition constituting the prepreg
contains the same quantity of resin particles as that specified in the particle content
list in Table 1.
(7) Proportion of particles existing in the region with a depth equal to 20% of the
prepreg thickness
[0160] The unidirectional prepreg prepared in section (4) is interposed between two polytetrafluoroethylene
resin plates with smooth surfaces and brought into close contact, then the temperature
is increased gradually for 7 days up to 150°C to ensure gelation and curing, thus
producing a plate-like cured resin. After the completion of curing, the cured body
was cut in a direction perpendicular to the contact interface, and the cross section
was polished and photographed with an optical microscope at a magnification of 200
or more in such a manner that the upper and lower surfaces of the prepreg were included
in the field of view. According to the same procedure, the distance between the polytetrafluoroethylene
resin plates was measured at five points aligned in the lateral direction in the cross-sectional
photograph, and the average (n=5) was assumed to represent the thickness of the prepreg.
For each of the two surfaces of the prepreg, a line parallel to the surface of the
prepreg was drawn at a depth equal to 20% of the thickness. Then, the total area of
the particles existing between each surface of the prepreg and each of the lines drawn
above and the total area of the particles existing across the entire thickness of
the prepreg were determined, followed by calculating the proportion of the number
of particles existing in the regions of 20% depth from the prepreg surfaces to the
total number of particles existing across the entire (100%) thickness of the prepreg.
Here, the total area of the fine particles was determined by cutting the particle
portions out of the cross-sectional photograph and converting their mass.
(8) Preparation of composite material plate for mode I interlaminar toughness (GIC)
test and implementation of GIC measurement
[0161] According to the following procedure from (a) to (e), composite material plates for
mode I interlaminar toughness (GIC) were test prepared according to JIS K7086 (1993).
- (a) A total of 20 unidirectional prepreg plies as prepared in section (6) were laminated
together with their fibers aligned in one direction. A fluorine resin film with a
width of 40 mm and a thickness of 50 µm was interposed at the center of the laminate
(between the 10th and the 11th ply) in such a manner that its direction was perpendicular
to the fibers.
- (b) The laminated prepreg plies were covered with a nylon film without leaving gaps,
and cured by pressing under heat in an autoclave at 180°C and internal pressure of
0.59 MPa for 2 hours to form a unidirectional fiber-reinforced composite material.
- (c) The unidirectional fiber-reinforced composite material obtained in step (b) was
cut to a width of 20 mm and a length of 195 mm. Cutting was performed so that the
fibers were parallel to the length direction of the specimen.
- (d) According to JIS K7086 (1993), a block (aluminum, length 25mm) for pin load application
was attached to an end (where the film was located) of the specimen.
- (e) White paint was applied to both side faces of the specimen to ensure easy observation
of the progress of cracking.
[0162] The composite material plate prepared above was used to make GIC measurements by
the following procedure.
[0163] Test was carried out using an Instron type universal tester (manufactured by Instron
Corporation) according to Appendix 1 of JIS K7086 (1993). The crosshead speed was
0.5 mm/min before the length of the crack reached 20 mm and 1 mm/min after it reached
20 mm. The GIC (GIC at the initial point of cracking) that corresponds to the critical
load at the initial point of cracking was calculated from the load, displacement,
and crack length according to JIS K7086 (1993).
(9) Measurement of mode II interlaminar toughness (GIIC)
[0164] The specimen preparation procedure described in steps (a) to (c) for GIC test in
section (8) was carried out to provide a specimen with a width of 20 mm and a length
of 195 mm. This specimen was subjected to ENF test according to Appendix 2 of JIS
K7086 (1993).
(10) Measurement of compressive strength under heat and humidity conditions of fiber-reinforced
composite material
[0165] A total of 12 unidirectional prepreg plies prepared in section (6) were laminated
with their fibers aligned parallel to the compression direction and heated in an autoclave
for 2 hours at a temperature of 180°C, a pressure of 0.59 MPa and a heating rate of
1.5°C/min to provide a laminate body. From this laminate body, a tabbed specimen with
a thickness of 2 mm, width of 15 mm, and length 78 mm was prepared and immersed in
warm water at 71°C for 14 days. This specimen was subjected to 0°compressive strength
measurement at 82°C using a universal tester equipped with a temperature controlled
bath according to JIS K7076 (1991). Five specimens were prepared (n=5).
(11) Measurement of interlayer thickness of fiber-reinforced composite material
[0166] A total of 20 unidirectional prepreg plies as prepared in section (4) were laminated
with their fibers aligned in one direction. The laminated prepreg plies were covered
with a nylon film without leaving gaps, and cured by pressing under heat in an autoclave
at 180°C and internal pressure of 0.59 MPa for 2 hours to form a unidirectional fiber-reinforced
composite material. This was cut in a direction perpendicular to the carbon fibers,
and the cross section was polished and photographed with an optical microscope at
a magnification of 200 or more. In an appropriately-selected region between fiber
layers in the photograph, a line parallel to the carbon fiber layers was drawn so
that it represented a carbon fiber volume content of 50%, and it was assumed to be
a boundary line between the internal region of the fiber layer and the interlayer
region between the fiber layers. A boundary line averaged over a length of 100 µm
was drawn, and the distance between them was assumed to represent the interlayer thickness.
The same procedure was carried out for five appropriately selected interlayer regions,
and the average was adopted.
(Example 1)
[0167] Using a kneader, the procedure specified in section (3) was carried out according
to the compounding ratios given in Table 1 to prepare an epoxy resin composition for
fiber-reinforced composite material production. For the resulting epoxy resin composition,
the procedures specified in section (4) "Measurement of bending elastic modulus of
cured resin" and (5) "Measurement of toughness (KIC) of cured resin" to determine
its bending elastic modulus and KIC. Elsewhere, the procedure specified in section
(6) was carried out to produce a prepreg in which particle 1 was extremely localized
near the surface. Using the resulting prepreg, the measurement procedures specified
in section (7) "Proportion of particles existing in the region with a depth equal
to 20% of the prepreg thickness", section (8) "Preparation of composite material plate
for mode I interlaminar toughness (GIC) test and implementation of GIC measurement",
section (9) "Measurement of mode II interlaminar toughness (GIIC)", section (10) "Measurement
of compressive strength under heat and humidity conditions of fiber-reinforced composite
material", and section (11) "Measurement of interlayer thickness of fiber-reinforced
composite material" were carried out.
[0168] Results are given in Table 1.
[0169] [Table 1]
[Table 1]
|
|
Examples |
Comparative examples |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
1 |
2 |
3 |
4 |
5 |
6 |
Components |
Epoxy resin [A] |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
other than |
○ELM434 |
|
60 |
60 |
50 |
50 |
50 |
10 |
60 |
50 |
10 |
50 |
50 |
50 |
50 |
50 |
10 |
resin particles |
○jER630 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
○MY0600 |
|
|
|
|
|
|
70 |
|
|
70 |
|
|
|
|
|
70 |
|
○GAN |
|
30 |
|
|
|
|
|
30 |
|
|
|
|
|
|
|
|
|
○GOT |
|
|
30 |
25 |
25 |
25 |
|
|
25 |
|
25 |
25 |
25 |
25 |
25 |
|
|
○jER828 |
60 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
○EPICLON 830 |
|
10 |
10 |
|
|
|
20 |
10 |
|
20 |
|
|
|
|
|
20 |
|
○EPICLON HP7200H |
40 |
|
|
25 |
25 |
25 |
|
|
25 |
|
25 |
25 |
25 |
25 |
25 |
|
|
Elastomer component [C] |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
○block copolymer M22N |
8 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
○block copolymer SM4032XM10 |
|
5 |
|
5 |
5 |
5 |
|
|
5 |
|
|
5 |
5 |
5 |
5 |
|
|
○core shell rubber particles MX416 |
|
|
5 |
|
|
|
5 |
5 |
|
5 |
|
|
|
|
|
|
|
Epoxy resin curing agent [D] |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
○Seikacure-S |
|
|
40 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
○3,3'-DAS |
40 |
40 |
|
40 |
40 |
40 |
40 |
40 |
40 |
40 |
40 |
40 |
40 |
40 |
40 |
40 |
|
Other component |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
○SnmikaAVrAI PFCS5003P |
|
|
10 |
|
|
|
15 |
|
|
|
|
|
|
|
|
15 |
Resin particles |
Resin particles [B] |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
○particles 1 |
20 |
20 |
20 |
20 |
|
|
20 |
20 |
|
20 |
20 |
|
|
|
|
20 |
|
○particles 2 |
|
|
|
|
20 |
|
|
|
|
|
|
|
|
|
|
|
|
○particles 3 |
|
|
|
|
|
20 |
|
|
|
|
|
|
|
|
|
|
|
○particles 4 |
|
|
|
|
|
|
|
|
20 |
|
|
|
|
|
|
|
|
Other resin particles |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
○particles 5 |
|
|
|
|
|
|
|
|
|
|
|
20 |
|
|
|
|
|
○particles 6 |
|
|
|
|
|
|
|
|
|
|
|
|
20 |
|
|
|
|
○particles 7 |
|
|
|
|
|
|
|
|
|
|
|
|
|
20 |
|
|
|
○particles 8 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
20 |
|
Particle content in total components (mass%) |
11.9 |
12.1 |
11.4 |
12.1 |
12.1 |
12.1 |
11.1 |
12.1 |
12.1 |
12.1 |
12.5 |
12.1 |
12.1 |
12.1 |
12.1 |
11.4 |
Characteristics of cured resin |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
○bending elastic modulus (MPa) |
3.5 |
3.8 |
3.4 |
3.9 |
3.9 |
3.9 |
4.0 |
3.7 |
3.9 |
4.1 |
4.0 |
4.0 |
3.9 |
3.9 |
3.8 |
4.2 |
○KIC (MPa·m0.5) |
1.5 |
1.0 |
0.9 |
1.2 |
1.1 |
1.1 |
1.0 |
1.0 |
1.0 |
0.9 |
0.7 |
0.9 |
1.1 |
1.0 |
1.1 |
0.6 |
Characteristics of fiber-reinforced composite material |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
○interlaminar toughness GIC (J/m2) |
770 |
680 |
630 |
790 |
710 |
660 |
650 |
660 |
610 |
650 |
490 |
390 |
440 |
560 |
620 |
460 |
○interlaminar toughness GIIC(J/m2) |
3300 |
3700 |
3400 |
3500 |
3300 |
3100 |
3200 |
3600 |
3300 |
3200 |
2900 |
2500 |
2300 |
2900 |
2800 |
2700 |
○open-hole compressive strength under heat and humidity conditions (MPa) |
1010 |
1140 |
1020 |
1160 |
1110 |
1100 |
1060 |
1120 |
1090 |
1000 |
1180 |
1130 |
920 |
1070 |
970 |
980 |
○interlayer thickness (µm) |
32 |
34 |
33 |
35 |
31 |
29 |
33 |
34 |
34 |
33 |
33 |
25 |
26 |
23 |
27 |
32 |
[0170] The basis weight resin of the film, particle content, and proportion of particles
existing in the region with a depth equal to 20% of the prepreg thickness are given
in Table 2.
[0171] [Table 2]
[Table 2]
|
Resin film for primary prepreg |
Resin film for two-step impregnation |
Prepreg |
|
Components other than resin particles |
Resin particles |
Basis weight of film |
Components other than resin particles |
Resin particles |
Content of resin particles |
Basis weight of film |
Content of resin particles*1 |
Proportion of particles localized near surface *2 |
|
|
|
(g/m2) |
|
|
(parts by mass) |
(mass%) |
(g/m2) |
(mass%) |
(%) |
Production example 1 |
Example 1 |
none |
30 |
Example 1 |
particle 1 |
62.7 |
29.8 |
20 |
11.9 |
97 |
Production example 2 |
Example 2 |
none |
30 |
Example 2 |
particle 1 |
63.0 |
30.3 |
20 |
12.1 |
98 |
Production example 3 |
Example 3 |
none |
30 |
Example 3 |
particle 1 |
63.0 |
30.3 |
20 |
12.1 |
97 |
Production example 4 |
Example 4 |
none |
30 |
Example 4 |
particle 1 |
63.0 |
30.3 |
20 |
12.1 |
98 |
Production example 5 |
Example 5 |
none |
30 |
Example 5 |
particle 2 |
63.0 |
30.3 |
20 |
12.1 |
95 |
Production example 6 |
Example 6 |
none |
30 |
Example 6 |
particle 3 |
63.0 |
30.3 |
20 |
12.1 |
94 |
Production example 7 |
Example 7 |
none |
30 |
Example 7 |
particle 4 |
63.0 |
30.3 |
20 |
12.1 |
97 |
Production example 8 |
Example 8 |
none |
30 |
Example 8 |
particle 1 |
63.0 |
30.3 |
20 |
12.1 |
96 |
Compative production example 1 |
Comparative example 1 |
none |
30 |
Comparative example 1 |
particle 1 |
63.6 |
31.3 |
20 |
12.5 |
98 |
Compative production example 2 |
Comparative example 2 |
none |
30 |
Comparative example 2 |
particle 5 |
63.0 |
30.3 |
20 |
12.1 |
91 |
Compative production example 3 |
Comparative example 3 |
none |
30 |
Comparative example 3 |
particle 6 |
63.0 |
30.3 |
20 |
12.1 |
96 |
Compative production example 4 |
Comparative example 4 |
none |
30 |
Comparative example 4 |
particle 7 |
63.0 |
30.3 |
20 |
12.1 |
93 |
Compative production example 5 |
Comparative example 5 |
none |
30 |
Comparative example 5 |
particle 8 |
63.0 |
30.3 |
20 |
12.1 |
96 |
Compative production example 6 |
Comparative example 6 |
none |
30 |
Comparative example 6 |
particle 1 |
61.8 |
28.5 |
20 |
12.1 |
97 |
*1 content of resin particles in total resin components in prepreg
*2 proportion of particles localized in 20% depth region from prepreg surface |
[0172] The prepreg had been impregnated appropriately and had good surface quality, and
the proportion of particles existing in the 20% depth region was a high 97%, showing
that resin particles were localized near the surface in the prepreg. Results show
that the fiber-reinforced composite material had a high GIC and GIIC as well as an
allowable compressive strength under heat and humidity conditions.
(Examples 2-10)
[0173] Except for using the compounding ratios specified in Table 1, the same procedure
as in Example 1 was carried out to provide epoxy resin compositions and prepregs.
Particles were localized adequately near the surface and the interlayer thicknesses
were adequately large, suggesting that the fiber-reinforced composite materials had
satisfactory values of GIC, GIIC and compressive strength under heat and humidity
conditions.
(Comparative example 1)
[0174] Except for using the compounding ratios specified in Table 1, the same procedure
as in Example 1 was carried out to provide an epoxy resin composition and prepreg.
Being free of elastomer component [C], the resulting cured resin was low in toughness
and the fiber-reinforced composite material was particularly low in GIC.
(Comparative examples 2 to 5)
[0175] Except for using particles unable to work as resin particles [B], the same procedure
as in Example 4 was carried out to provide epoxy resin compositions and prepregs.
These particles did not meet the requirements of (b1) to (b3) and could not have satisfactory
values for all GIC, GIIC and compressive strength under heat and humidity conditions.
(Comparative example 6)
[0176] Except for using the compounding ratios specified in Table 1, the same procedure
as in Example 1 was carried out to provide an epoxy resin composition and prepreg.
Due to the addition of polyethersulfone instead of component [C], the resulting cured
resin was low in toughness and the fiber-reinforced composite material was particularly
low in GIC.
[Industrial applicability]
[0177] According to the present invention, it is possible to provide fiber-reinforced composite
materials having a high mode I interlaminar toughness, high mode II interlaminar toughness,
and high compression strength under heat and humidity conditions, and they can serve
effectively for production of structural members. Their preferred applications in
the aerospace industry include, for instance, primary structural members of aircraft
such as main wing, tail unit, and floor beam; secondary structural members such as
flap, aileron, cowl, fairing, and other interior materials, and structural members
of artificial satellites such as rocket motor case. Their preferred applications for
general industrial uses include structural members of vehicles such as automobile,
ship, and railroad vehicle; and civil engineering and construction materials such
as drive shaft, plate spring, windmill blade, various turbines, pressure vessel, flywheel,
roller for paper manufacture, roofing material, cable, reinforcing bar, and mending/reinforcing
materials. Applications in the sporting goods industry include golf shaft, fishing
pole, rackets for tennis, badminton, squash, etc., hockey stick, and skiing pole.